As promised, there is some discussion of setting gamma toward the end of this thread:
Unfortunately, Shotcut’s scope lacks the graticule lines needed to do this really right. You need graticule lines at digital 235, digital 111 and digital 16. I cheated by writing my own scope code. Contact me if you are interested in it.
Or, you could make gray patches at 235, 111 and 16 and get Shotcut to make you a split screen between your camera video and the gray patches and try to match them visually. Obviously you would make adjustments to your camera video and not the gray patches.